Abstract:
Exserohilum turcicum is a foliar pathogen that causes the widespread and damaging
disease, northern leaf blight (NLB), in both sorghum and maize. Even though E.
turcicum is an economically important pathogen, limited information is available on
the underlying molecular mechanisms of the sorghum-E. turcicum interaction and,
more specifically, the sorghum response. This study aimed to gain insight into the
sorghum response to E. turcicum infection. A real-time quantitative PCR (qPCR)
assay was developed that specifically detects and accurately quantifies the relative
E. turcicum DNA present in infected sorghum and maize leaf samples. The qPCR
assay was applied to quantify E. turcicum DNA in sorghum and maize leaf samples
across NLB disease stages. Pathogenicity trials in commercial sorghum and maize
varieties with varying degrees of NLB resistance were undertaken to show that the
sorghum E. turcicum isolate 73 is only pathogenic on sorghum. The pathogenic
specialization of the sorghum E. turcicum isolate was based on visual disease
symptoms and in planta fungal biomass that was determined through the E.
turcicum qPCR assay. Transcriptomic characterization of the sorghum response to E.
turcicum infection was done through RNA sequencing of two time points of a
moderately resistant sorghum-E. turcicum interaction. Differential expression
analysis of the RNA-Seq data revealed the significant downregulation of the Sb-
THI1-1 and Sb-THI1-2 thiamine biosynthesis gene targets after E. turcicum
inoculation. Sorghum putative Sb-THIC and Sb-COG0212 genes were also
identified. The sorghum targets putatively involved in thiamine metabolism as well
as sorghum putative resistance genes were analyzed through RT-qPCR analysis.
Research from this study will positively impact NLB resistance breeding efforts for
effective disease management.
